ABSTRACT Many trigger point therapies, such as deep pressure massage and injection, are painful. Thermal ultrasound might be a comfortable procedure used to soften trigger points. Our objective was to compare thermal ultrasound with sham ultrasound in the ability to soften trigger points with pretest/posttest repeated-measures design for depth of tissue in a massage therapy clinic. Twenty-six patients with latent trigger points in their upper trapezius muscles were studied. Independent variables were treatments; dependent variables were tissue depth. Subjects were randomly assigned to either the treatment or sham group. The study was single-blinded; the investigator taking the measurements was blinded to which group the subjects were in, and the clinician treating with ultrasound was blinded to the measurements. Each trigger point in the treatment group received 3 MHz ultrasound at the following parameters: 1.4 W/cm(2), 5 min, circular motion, 2x the size of the 7 cm(2) soundhead. The ultrasound was not turned on for the sham group. This procedure was repeated one week later. Trigger point depth was measured with a pressure algometer before and immediately after each treatment. A 2 x 2 x 2 repeated measures ANOVA was used to analyze depth (mm). The immediate effects were as follows: The mean depth value for the sham group was an increase of 0.64+/-0.33 mm; the treatment group's mean increase was 2.65+/-0.33 mm (F(1,24)=19.01; p=0.01). The residual effects were as follows: The two treatments over the course of the 2 weeks also showed that the trigger points of the ultrasound groups got softer with an increase in depth of 2.09+/-0.82 mm compared to -0.93+/-0.82 mm of the sham group (F(1,24)=6.81; p<0.01). Thermal ultrasound over latent trigger points is comfortable and can decrease stiffness of a trigger point.